On Thu, Oct 27, 2011 at 9:54 PM, Martin Jambor <[email protected]> wrote:
> Hi,
>
> On Thu, Oct 27, 2011 at 11:06:02AM +0200, Richard Guenther wrote:
>> On Thu, Oct 27, 2011 at 1:22 AM, Martin Jambor <[email protected]> wrote:
>> > Hi,
>> >
>> > I've been asked by Maxim Kuvyrkov to revive the following patch which
>> > has not made it to 4.6. Currently, when type based devirtualization
>> > detects a potential type change, it simply gives up on gathering any
>> > information on the object in question. This patch adds an attempt to
>> > actually detect the new type after the change.
>> >
>> > Maxim claimed this (and another patch I'll post tomorrow) noticeably
>> > improved performance of some real code. I can only offer a rather
>> > artificial example in the attachment. When the constructors are
>> > inlined but the function multiply_matrices is not, this patch makes
>> > the produced executable run for only 7 seconds instead of about 20 on
>> > my 4 year old i686 desktop (with -Ofast).
>> >
>> > Anyway, the patch passes bootstrap and testsuite on x86_64-linux.
>> > What do you think, is it a good idea for trunk now?
>> >
>> > Thanks,
>> >
>> > Martin
>> >
>> >
>> > 2011-10-21 Martin Jambor <[email protected]>
>> >
>> > * ipa-prop.c (type_change_info): New fields object,
>> > known_current_type
>> > and multiple_types_encountered.
>> > (extr_type_from_vtbl_ptr_store): New function.
>> > (check_stmt_for_type_change): Use it, set
>> > multiple_types_encountered if
>> > the result is different from the previous one.
>> > (detect_type_change): Renamed to detect_type_change_1. New parameter
>> > comp_type. Set up new fields in tci, build known type jump
>> > functions if the new type can be identified.
>> > (detect_type_change): New function.
>> > * tree.h (DECL_CONTEXT): Comment new use.
>> >
>> > * testsuite/g++.dg/ipa/devirt-c-1.C: Add dump scans.
>> > * testsuite/g++.dg/ipa/devirt-c-2.C: Likewise.
>> > * testsuite/g++.dg/ipa/devirt-c-7.C: New test.
>> >
>> >
>> > Index: src/gcc/ipa-prop.c
>> > ===================================================================
>> > --- src.orig/gcc/ipa-prop.c
>> > +++ src/gcc/ipa-prop.c
>> > @@ -271,8 +271,17 @@ ipa_print_all_jump_functions (FILE *f)
>> >
>> > struct type_change_info
>> > {
>> > + /* The declaration or SSA_NAME pointer of the base that we are checking
>> > for
>> > + type change. */
>> > + tree object;
>> > + /* If we actually can tell the type that the object has changed to, it
>> > is
>> > + stored in this field. Otherwise it remains NULL_TREE. */
>> > + tree known_current_type;
>> > /* Set to true if dynamic type change has been detected. */
>> > bool type_maybe_changed;
>> > + /* Set to true if multiple types have been encountered.
>> > known_current_type
>> > + must be disregarded in that case. */
>> > + bool multiple_types_encountered;
>> > };
>> >
>> > /* Return true if STMT can modify a virtual method table pointer.
>> > @@ -338,6 +347,49 @@ stmt_may_be_vtbl_ptr_store (gimple stmt)
>> > return true;
>> > }
>> >
>> > +/* If STMT can be proved to be an assignment to the virtual method table
>> > + pointer of ANALYZED_OBJ and the type associated with the new table
>> > + identified, return the type. Otherwise return NULL_TREE. */
>> > +
>> > +static tree
>> > +extr_type_from_vtbl_ptr_store (gimple stmt, tree analyzed_obj)
>> > +{
>> > + tree lhs, t, obj;
>> > +
>> > + if (!is_gimple_assign (stmt))
>>
>> gimple_assign_single_p (stmt)
>
> OK.
>
>>
>> > + return NULL_TREE;
>> > +
>> > + lhs = gimple_assign_lhs (stmt);
>> > +
>> > + if (TREE_CODE (lhs) != COMPONENT_REF)
>> > + return NULL_TREE;
>> > + obj = lhs;
>> > +
>> > + if (!DECL_VIRTUAL_P (TREE_OPERAND (lhs, 1)))
>> > + return NULL_TREE;
>> > +
>> > + do
>> > + {
>> > + obj = TREE_OPERAND (obj, 0);
>> > + }
>> > + while (TREE_CODE (obj) == COMPONENT_REF);
>>
>> You do not allow other components than component-refs (thus, for
>> example an ARRAY_REF - that is for a reason?). Please add
>> a comment why. Otherwise this whole sequence would look like
>> it should be replaceable by get_base_address (obj).
>>
>
> I guess I might have been overly conservative here, ARRAY_REFs are
> fine. get_base_address only digs into MEM_REFs if they are based on
> an ADDR_EXPR while I do so always. But I can check that either both
> obj and analyzed_obj are a MEM_REF of the same SSA_NAME or they are
> the same thing (i.e. the same decl)... which even feels a bit cleaner,
> so I did that.
Well, as you are looking for a must-change-type pattern I think you cannot
simply ignore offsets. Consider
T a[10];
new (T') (&a[9]);
a[8]->foo();
where the must-type-change on a[9] is _not_ changing the type of a[8]!
Similar cases might happen with
class Compound { T a; T b; };
no?
Please think about the difference must vs. may-type-change for these
cases. I'm not convinced that the must-type-change code is correct.
Richard.
>
>> > + if (TREE_CODE (obj) == MEM_REF)
>> > + obj = TREE_OPERAND (obj, 0);
>> > + if (TREE_CODE (obj) == ADDR_EXPR)
>> > + obj = TREE_OPERAND (obj, 0);
>> > + if (obj != analyzed_obj)
>> > + return NULL_TREE;
>> > +
>> > + t = gimple_assign_rhs1 (stmt);
>> > + if (TREE_CODE (t) != ADDR_EXPR)
>> > + return NULL_TREE;
>> > + t = get_base_address (TREE_OPERAND (t, 0));
>>
>> Do we actually ever store sth else than the plain address of a
>> virtual table (thus, &decl)? If so, what difference makes the offset
>> into the virtual table we get in this way? I ask, because ...
>>
>> > + if (!t || TREE_CODE (t) != VAR_DECL || !DECL_VIRTUAL_P (t))
>> > + return NULL_TREE;
>> > +
>> > + return DECL_CONTEXT (t);
>>
>> ... DECL_CONTEXT (t) is of course independent of any offset.
>>
>> Thus I think you should drop the call to get_base_address () and
>> instead just look at TREE_OPERAND (t, 0).
>
> Even the simplest cases of assignments have basically a form like
> this:
>
> this_1(D)->_vptr.A = &MEM[(void *)&_ZTV1A + 8B];
>
> so I need to extract the actual VAR_DECL somehow. But of course I can
> do that by looking through the MEM_REF and ADDR_EXPR by hand, if
> preferable.
>
>>
>> > +}
>> > +
>> > /* Callback of walk_aliased_vdefs and a helper function for
>> > detect_type_change to check whether a particular statement may modify
>> > the virtual table pointer, and if possible also determine the new type
>> > of
>> > @@ -352,6 +404,12 @@ check_stmt_for_type_change (ao_ref *ao A
>> >
>> > if (stmt_may_be_vtbl_ptr_store (stmt))
>> > {
>> > + tree type;
>> > + type = extr_type_from_vtbl_ptr_store (stmt, tci->object);
>> > + if (tci->type_maybe_changed
>> > + && type != tci->known_current_type)
>> > + tci->multiple_types_encountered = true;
>> > + tci->known_current_type = type;
>> > tci->type_maybe_changed = true;
>> > return true;
>> > }
>> > @@ -359,19 +417,19 @@ check_stmt_for_type_change (ao_ref *ao A
>> > return false;
>> > }
>> >
>> > -/* Detect whether the dynamic type of ARG has changed (before callsite
>> > CALL) by
>> > - looking for assignments to its virtual table pointer. If it is,
>> > return true
>> > - and fill in the jump function JFUNC with relevant type information or
>> > set it
>> > - to unknown. ARG is the object itself (not a pointer to it, unless
>> > - dereferenced). BASE is the base of the memory access as returned by
>> > - get_ref_base_and_extent, as is the offset. */
>> > +
>> > +
>> > +/* Like detect_type_change but with extra argument COMP_TYPE which will
>> > become
>> > + the component type part of new JFUNC of dynamic type change is
>> > detected and
>> > + the new base type is identified. */
>> >
>> > static bool
>> > -detect_type_change (tree arg, tree base, gimple call,
>> > - struct ipa_jump_func *jfunc, HOST_WIDE_INT offset)
>> > +detect_type_change_1 (tree arg, tree base, tree comp_type, gimple call,
>> > + struct ipa_jump_func *jfunc, HOST_WIDE_INT offset)
>> > {
>> > struct type_change_info tci;
>> > ao_ref ao;
>> > + tree t;
>> >
>> > gcc_checking_assert (DECL_P (arg)
>> > || TREE_CODE (arg) == MEM_REF
>> > @@ -381,8 +439,6 @@ detect_type_change (tree arg, tree base,
>> > if (!flag_devirtualize || !gimple_vuse (call))
>> > return false;
>> >
>> > - tci.type_maybe_changed = false;
>> > -
>> > ao.ref = arg;
>> > ao.base = base;
>> > ao.offset = offset;
>> > @@ -391,15 +447,51 @@ detect_type_change (tree arg, tree base,
>> > ao.ref_alias_set = -1;
>> > ao.base_alias_set = -1;
>> >
>> > + t = arg;
>> > + while (handled_component_p (t))
>> > + t = TREE_OPERAND (t, 0);
>>
>> Here you are using handled_component_p, thus allow ARRAY_REFs ...
>> but you are not trying to distinguish a[1] from a[2] anywhere, so this
>> looks bogus and instead should look like the case above (with a comment
>> as to why looking at ARRAY_REFs would be bogus).
>
> I changed both to get_base_address as described above.
>
> This is the new version of the patch which I'm currently bootstrapping
> and testing on an x86_64-linux. OK for trunk if it passes? Thanks.
>
> Martin
>
>
> 2011-10-27 Martin Jambor <[email protected]>
>
> * ipa-prop.c (type_change_info): New fields object, known_current_type
> and multiple_types_encountered.
> (extr_type_from_vtbl_ptr_store): New function.
> (check_stmt_for_type_change): Use it, set multiple_types_encountered if
> the result is different from the previous one.
> (detect_type_change): Renamed to detect_type_change_1. New parameter
> comp_type. Set up new fields in tci, build known type jump
> functions if the new type can be identified.
> (detect_type_change): New function.
> * tree.h (DECL_CONTEXT): Comment new use.
>
> * testsuite/g++.dg/ipa/devirt-c-1.C: Add dump scans.
> * testsuite/g++.dg/ipa/devirt-c-2.C: Likewise.
> * testsuite/g++.dg/ipa/devirt-c-7.C: New test.
>
>
> Index: src/gcc/ipa-prop.c
> ===================================================================
> --- src.orig/gcc/ipa-prop.c
> +++ src/gcc/ipa-prop.c
> @@ -271,8 +271,17 @@ ipa_print_all_jump_functions (FILE *f)
>
> struct type_change_info
> {
> + /* The declaration or SSA_NAME pointer of the base that we are checking for
> + type change. */
> + tree object;
> + /* If we actually can tell the type that the object has changed to, it is
> + stored in this field. Otherwise it remains NULL_TREE. */
> + tree known_current_type;
> /* Set to true if dynamic type change has been detected. */
> bool type_maybe_changed;
> + /* Set to true if multiple types have been encountered. known_current_type
> + must be disregarded in that case. */
> + bool multiple_types_encountered;
> };
>
> /* Return true if STMT can modify a virtual method table pointer.
> @@ -338,6 +347,44 @@ stmt_may_be_vtbl_ptr_store (gimple stmt)
> return true;
> }
>
> +/* If STMT can be proved to be an assignment to the virtual method table
> + pointer of ANALYZED_OBJ and the type associated with the new table
> + identified, return the type. Otherwise return NULL_TREE. */
> +
> +static tree
> +extr_type_from_vtbl_ptr_store (gimple stmt, tree analyzed_obj)
> +{
> + tree lhs, t, obj;
> +
> + if (!gimple_assign_single_p (stmt))
> + return NULL_TREE;
> +
> + lhs = gimple_assign_lhs (stmt);
> +
> + if (TREE_CODE (lhs) != COMPONENT_REF
> + || !DECL_VIRTUAL_P (TREE_OPERAND (lhs, 1)))
> + return NULL_TREE;
> +
> + obj = get_base_address (lhs);
> + if (TREE_CODE (obj) == MEM_REF)
> + {
> + if (TREE_CODE (analyzed_obj) != MEM_REF
> + || TREE_OPERAND (analyzed_obj, 0) != TREE_OPERAND (obj, 0))
> + return NULL_TREE;
> + }
> + else if (analyzed_obj != obj)
> + return NULL_TREE;
> +
> + t = gimple_assign_rhs1 (stmt);
> + if (TREE_CODE (t) != ADDR_EXPR)
> + return NULL_TREE;
> + t = get_base_address (TREE_OPERAND (t, 0));
> + if (!t || TREE_CODE (t) != VAR_DECL || !DECL_VIRTUAL_P (t))
> + return NULL_TREE;
> +
> + return DECL_CONTEXT (t);
> +}
> +
> /* Callback of walk_aliased_vdefs and a helper function for
> detect_type_change to check whether a particular statement may modify
> the virtual table pointer, and if possible also determine the new type of
> @@ -352,6 +399,12 @@ check_stmt_for_type_change (ao_ref *ao A
>
> if (stmt_may_be_vtbl_ptr_store (stmt))
> {
> + tree type;
> + type = extr_type_from_vtbl_ptr_store (stmt, tci->object);
> + if (tci->type_maybe_changed
> + && type != tci->known_current_type)
> + tci->multiple_types_encountered = true;
> + tci->known_current_type = type;
> tci->type_maybe_changed = true;
> return true;
> }
> @@ -359,16 +412,15 @@ check_stmt_for_type_change (ao_ref *ao A
> return false;
> }
>
> -/* Detect whether the dynamic type of ARG has changed (before callsite CALL)
> by
> - looking for assignments to its virtual table pointer. If it is, return
> true
> - and fill in the jump function JFUNC with relevant type information or set
> it
> - to unknown. ARG is the object itself (not a pointer to it, unless
> - dereferenced). BASE is the base of the memory access as returned by
> - get_ref_base_and_extent, as is the offset. */
> +
> +
> +/* Like detect_type_change but with extra argument COMP_TYPE which will
> become
> + the component type part of new JFUNC of dynamic type change is detected
> and
> + the new base type is identified. */
>
> static bool
> -detect_type_change (tree arg, tree base, gimple call,
> - struct ipa_jump_func *jfunc, HOST_WIDE_INT offset)
> +detect_type_change_1 (tree arg, tree base, tree comp_type, gimple call,
> + struct ipa_jump_func *jfunc, HOST_WIDE_INT offset)
> {
> struct type_change_info tci;
> ao_ref ao;
> @@ -381,8 +433,6 @@ detect_type_change (tree arg, tree base,
> if (!flag_devirtualize || !gimple_vuse (call))
> return false;
>
> - tci.type_maybe_changed = false;
> -
> ao.ref = arg;
> ao.base = base;
> ao.offset = offset;
> @@ -391,15 +441,44 @@ detect_type_change (tree arg, tree base,
> ao.ref_alias_set = -1;
> ao.base_alias_set = -1;
>
> + tci.object = get_base_address (arg);
> + tci.known_current_type = NULL_TREE;
> + tci.type_maybe_changed = false;
> + tci.multiple_types_encountered = false;
> +
> walk_aliased_vdefs (&ao, gimple_vuse (call), check_stmt_for_type_change,
> &tci, NULL);
> if (!tci.type_maybe_changed)
> return false;
>
> - jfunc->type = IPA_JF_UNKNOWN;
> + if (!tci.known_current_type
> + || tci.multiple_types_encountered
> + || offset != 0)
> + jfunc->type = IPA_JF_UNKNOWN;
> + else
> + {
> + jfunc->type = IPA_JF_KNOWN_TYPE;
> + jfunc->value.known_type.base_type = tci.known_current_type;
> + jfunc->value.known_type.component_type = comp_type;
> + }
> +
> return true;
> }
>
> +/* Detect whether the dynamic type of ARG has changed (before callsite CALL)
> by
> + looking for assignments to its virtual table pointer. If it is, return
> true
> + and fill in the jump function JFUNC with relevant type information or set
> it
> + to unknown. ARG is the object itself (not a pointer to it, unless
> + dereferenced). BASE is the base of the memory access as returned by
> + get_ref_base_and_extent, as is the offset. */
> +
> +static bool
> +detect_type_change (tree arg, tree base, gimple call,
> + struct ipa_jump_func *jfunc, HOST_WIDE_INT offset)
> +{
> + return detect_type_change_1 (arg, base, TREE_TYPE (arg), call, jfunc,
> offset);
> +}
> +
> /* Like detect_type_change but ARG is supposed to be a non-dereferenced
> pointer
> SSA name (its dereference will become the base and the offset is assumed to
> be zero). */
> @@ -407,16 +486,19 @@ detect_type_change (tree arg, tree base,
> static bool
> detect_type_change_ssa (tree arg, gimple call, struct ipa_jump_func *jfunc)
> {
> + tree comp_type;
> +
> gcc_checking_assert (TREE_CODE (arg) == SSA_NAME);
> if (!flag_devirtualize
> || !POINTER_TYPE_P (TREE_TYPE (arg))
> || TREE_CODE (TREE_TYPE (TREE_TYPE (arg))) != RECORD_TYPE)
> return false;
>
> + comp_type = TREE_TYPE (TREE_TYPE (arg));
> arg = build2 (MEM_REF, ptr_type_node, arg,
> - build_int_cst (ptr_type_node, 0));
> + build_int_cst (ptr_type_node, 0));
>
> - return detect_type_change (arg, arg, call, jfunc, 0);
> + return detect_type_change_1 (arg, arg, comp_type, call, jfunc, 0);
> }
>
> /* Callback of walk_aliased_vdefs. Flags that it has been invoked to the
> Index: src/gcc/testsuite/g++.dg/ipa/devirt-c-1.C
> ===================================================================
> --- src.orig/gcc/testsuite/g++.dg/ipa/devirt-c-1.C
> +++ src/gcc/testsuite/g++.dg/ipa/devirt-c-1.C
> @@ -1,7 +1,7 @@
> /* Verify that ipa-cp correctly detects the dynamic type of an object
> under construction when doing devirtualization. */
> /* { dg-do run } */
> -/* { dg-options "-O3 -fno-early-inlining -fno-inline" } */
> +/* { dg-options "-O3 -fno-early-inlining -fno-inline -fdump-ipa-cp
> -fdump-tree-optimized" } */
>
> extern "C" void abort (void);
>
> @@ -69,3 +69,8 @@ int main (int argc, char *argv[])
> bah ();
> return 0;
> }
> +
> +/* { dg-final { scan-ipa-dump "Discovered a virtual call to a known
> target.*A::foo" "cp" } } */
> +/* { dg-final { scan-tree-dump-times "OBJ_TYPE_REF" 0 "optimized"} } */
> +/* { dg-final { cleanup-ipa-dump "cp" } } */
> +/* { dg-final { cleanup-tree-dump "optimized" } } */
> Index: src/gcc/testsuite/g++.dg/ipa/devirt-c-2.C
> ===================================================================
> --- src.orig/gcc/testsuite/g++.dg/ipa/devirt-c-2.C
> +++ src/gcc/testsuite/g++.dg/ipa/devirt-c-2.C
> @@ -1,7 +1,7 @@
> /* Verify that ipa-cp correctly detects the dynamic type of an object
> under construction when doing devirtualization. */
> /* { dg-do run } */
> -/* { dg-options "-O3 -fno-early-inlining -fno-inline" } */
> +/* { dg-options "-O3 -fno-early-inlining -fno-inline -fdump-ipa-cp
> -fdump-tree-optimized" } */
>
> extern "C" void abort (void);
>
> @@ -77,3 +77,8 @@ int main (int argc, char *argv[])
> bah ();
> return 0;
> }
> +
> +/* { dg-final { scan-ipa-dump "Discovered a virtual call to a known
> target.*A::foo" "cp" } } */
> +/* { dg-final { scan-tree-dump-times "OBJ_TYPE_REF" 0 "optimized"} } */
> +/* { dg-final { cleanup-ipa-dump "cp" } } */
> +/* { dg-final { cleanup-tree-dump "optimized" } } */
> Index: src/gcc/tree.h
> ===================================================================
> --- src.orig/gcc/tree.h
> +++ src/gcc/tree.h
> @@ -2678,7 +2678,9 @@ struct function;
> nodes, this points to either the FUNCTION_DECL for the containing
> function, the RECORD_TYPE or UNION_TYPE for the containing type, or
> NULL_TREE or a TRANSLATION_UNIT_DECL if the given decl has "file
> - scope". */
> + scope". In particular, for VAR_DECLs which are virtual table pointers
> + (they have DECL_VIRTUAL set), we use DECL_CONTEXT to determine the type
> + they belong to. */
> #define DECL_CONTEXT(NODE) (DECL_MINIMAL_CHECK (NODE)->decl_minimal.context)
> #define DECL_FIELD_CONTEXT(NODE) \
> (FIELD_DECL_CHECK (NODE)->decl_minimal.context)
> Index: src/gcc/testsuite/g++.dg/ipa/devirt-c-7.C
> ===================================================================
> --- /dev/null
> +++ src/gcc/testsuite/g++.dg/ipa/devirt-c-7.C
> @@ -0,0 +1,87 @@
> +/* Verify that ipa-cp will not get confused by placement new constructing an
> + object within another one when looking for dynamic type change . */
> +/* { dg-do run } */
> +/* { dg-options "-O3 -Wno-attributes" } */
> +
> +extern "C" void abort (void);
> +namespace std {
> + typedef __SIZE_TYPE__ size_t;
> +}
> +inline void* __attribute__ ((always_inline))
> +operator new(std::size_t, void* __p) throw()
> +{
> + return __p;
> +}
> +
> +class A
> +{
> +public:
> + char data[256];
> + A();
> + virtual int foo (int i);
> +};
> +
> +class B : public A
> +{
> +public:
> + virtual int foo (int i);
> +};
> +
> +class C
> +{
> +public:
> + C();
> + virtual double foo (double i);
> +};
> +
> +int A::foo (int i)
> +{
> + return i + 1;
> +}
> +
> +int B::foo (int i)
> +{
> + return i + 2;
> +}
> +
> +double C::foo (double i)
> +{
> + return i + 3.5;
> +}
> +
> +static int __attribute__ ((noinline)) middleman (class A *obj, int i)
> +{
> + return obj->foo (i);
> +}
> +
> +int __attribute__ ((noinline,noclone)) get_input(void)
> +{
> + return 1;
> +}
> +
> +__attribute__ ((always_inline)) C::C ()
> +{
> +}
> +
> +A::A ()
> +{
> +}
> +
> +static __attribute__ ((noinline)) void bah ()
> +{
> + class B b;
> +
> + C *c = new ((void *) &b.data) C;
> +
> + if (middleman (&b, get_input ()) != 3)
> + abort ();
> +}
> +
> +int main (int argc, char *argv[])
> +{
> + int i;
> +
> + for (i = 0; i < 10; i++)
> + bah ();
> + return 0;
> +}
>
